Reviewing the part number listings it appears that the correct levers for the MP3 500 from 2016 onwards are 1C001294 (same for front and rear brake).
Will anyone know what other part numbers are compatible?
It's hard for me to believe that only this 1C001294 lever model works and that there aren't other Piaggio/Vespa/Aprilia models that don't use levers compatible with the master cylinders used by MP3s. Or in other words, that MP3s use an exclusive master cylinder for them.
Any insight?